Classic aircraft production has, since early in the history of hard-skinned aerostructures, involved making templates and aligning them on fuselage and flight surface skins, then drilling through holes in the templates using hand-held drills to prepare the aerostructure for installation of rivets and screws. Placement of holes in the structure has thus generally been limited to human speeds, and has required extensive inspection.
In theory, a massive robotic apparatus could be developed that could autonomously place holes at any location on a workpiece such as an aerostructure, with the robotic apparatus placed, for example, on a monument base separated from the workpiece, and with each hole drilled with accuracy limited by the position sensors in the robotic apparatus. Such apparatus, however, has not been developed or shown to be economically feasible for general use. However, it has been demonstrated that a manufacturing apparatus with some degree of automation, attached directly to a portion of a workpiece under construction, can be practical, where desirable criteria of practicality include accuracy, adaptability, speed, low manufacturing cost, and light weight and compact size for ease of positioning,.
For generally flat and/or straight surfaces, which can occur, in a limited number of cases, along the longitudinal axis of a fuselage, a variety of robotic tools can be effective. For example, in an early version, a substantially rigid rail was temporarily attached to a workpiece using common fasteners such as screws. A drill could be moved along the rail, by hand or using a motorized positioner, to successive locations adjacent to the rail, at which locations the drill could be caused to drill a clean, straight hole. The drill could then be advanced until all of the needed holes along that straight line had been drilled.
The process and apparatus described above has strengths, namely that a series of holes can be drilled with quite good precision and decent speed, but also has several drawbacks. For example, there must first be correctly located mounting holes to which to attach the rail. Further, installation and removal of the rail may easily mar the workpiece. Also, alignment is critical and may be time-consuming. As well, only a small percentage of needed holes are likely to fall on any one line, so devising the drilling patterns, preparing mounting holes, and repeatedly repositioning the rail can be tedious. In addition, as noted, a rigid rail cannot traverse curves, so the above-described tool could not be positioned circumferentially on fuselages, for example, or typically in any direction other than spanwise on wings.
An additional drawback, not only to the apparatus described above but to other apparatus in existence, involves limited excursion range for a drilling component of the apparatus. Typical tools may use two rails to provide a secure base, then translate a toolhead across a workpiece. Even if the toolhead can move between the rails as well as along the rails, no work can be performed outside an excursion envelope established by the two rails.
Accordingly, it is desirable to provide a flexible rail machine tool method and apparatus that conforms to a workpiece surface that may have significant curvature, which flexible rail machine tool can drill holes within a work zone on the workpiece. It is further desirable that such a tool be able to traverse a surface along at lease one axis without manual repositioning and to drill holes normal to a surface substantially without manual intervention. It is further desirable that such a tool be able to drill holes outside the excursion envelope defined by the rail system attachment footprint. It is further desirable that such a tool be able to translate desired hole locations from a reference coordinate system to an as-affixed coordinate system. It is further desirable that such a tool be readily mounted and demounted from the workpiece.